Analysis of nonblocking ATM switches with multiple input queues

An analytical model for the performance analysis of a multiple input queued asynchronous transfer mode (ATM) switch is presented. The interconnection network of the ATM switch is internally nonblocking and each input port maintains a separate queue of cells for each output port. The switch uses parallel iterative matching (PIM) to find the maximal matching between the input and output ports of the switch. A closed-form solution for the maximum throughput of the switch under saturated conditions is derived. It is found that the maximum throughput of the switch exceeds 99% with just four iterations of the PIM algorithm. Using the tagged input queue approach, an analytical model for evaluating the switch performance under an independent identically distributed Bernoulli traffic with the cell destinations uniformly distributed over all output ports is developed. The switch throughput, mean cell delay, and cell loss probability are computed from the analytical model. The accuracy of the analytical model is verified using simulation     

Embedding Pyramids into 3D Meshes

The pyramid architecture is a powerful topology in the area of computer vision. On the other hand, the 3D mesh architecture possesses rich topological features which make it suitable for building scalable parallel processor systems. The usefulness of these two architectures has led us to consider the problem of embedding pyramids into 3D meshes, for which we present two solutions. The first solution, termednatural embedding,maps a pyramid into a 3D mesh such that each level of the pyramid is mapped to a single level of the 3D mesh. The second solution, termedmultiple embedding,allows simultaneous embedding of multiple pyramids into a single 3D mesh. The quality of both solutions is evaluated using dilation and expansion measures. Using the multiple embedding, we are able to obtain an average dilation of 1.26 and a near-optimal expansion of 1.12.     

Changes in membrane fatty acids and murein composition of Bacillus cereus and Salmonella Typhi induced by gamma irradiation treatment

This present study was carried out to evaluate the effects of gamma irradiation on the fatty acids (FA) and mureins composition of two different radiotolerant bacteria. Bacillus cereus LSPQ 2872 and Salmonella Typhi ATCC 19430 were used for this study. The bacterial strains were treated with a sublethal radiation dose of 1 kGy to cause a cellular damage. Gas chromatography (GC) and high performance liquid chromatography (HPLC) analysis were performed to demonstrate respectively the modification of the FA composition and the changes in muropeptide profile. Results obtained show, for both bacteria, that this treatment had a significant effect (P ≤ 0.05) on the FA content with an increase of unsaturated FA percentage. Substantial changes were also noticed for the relative percentage and the number of the muropeptides. This study represents one of the few to demonstrate the modifications on bacterial membrane as a cellular response to survive the ionising radiation stress.     

Enhancement of fermentative hydrogen production by Thermotoga maritima through hyperthermophilic anaerobic co-digestion of fruit-vegetable and fish wastes

In this work, different proportions of model fruit and vegetable wastes (MFVW) and acid hydrolyzed fish wastes (AHFW) were used for hydrogen production in a minimum culture medium based on seawater. Experiments were performed in pH-controlled Stirred Tank Reactor (STR) with or without the addition of nitrogen and sulfur sources. The total H₂ production and the maximum hydrogen productivity of T. maritima in the culture medium, containing MFVW and AHFW (45 mmol L^?1 carbohydrates) at a C/N ratio of 12, were 132 mmol L^?1 and 15 mmol h^?1 L^?1, respectively. However, tripling the concentration of carbohydrates to reach a C/N ratio of 22, has increased two times the maximum H₂ productivity (28 mmol h^?1 L^?1) due to the improvement in nutrient balance. The cumulative H₂ production was 285 mmol L^?1, yielding a potential energy generation of 0.1210³ MJ ton^?1 wastes, which could be an interesting alternative for energy recovery.     

Numerical Analysis of Heat Transfer and Nanofluid Flow in a Triangular Duct with Vortex Generator: Two‐Phase Model

Laminar forced convection heat transfer and nanofluids flow in an equilateral triangular channel using a delta‐winglet pair of vortex generators is numerically studied. Three nanofluids, namely; Al₂O₃, CuO, and SiO₂ nanoparticles suspended in an ethylene glycol base fluid are examined. A two‐phase mixture model is considered to simulate the governing equations of mass, momentum and energy for both phases and solved using the finite volume method (FVM). Constant and temperature dependent properties methods are assumed. The single‐phase model is considered here for comparison. The nanoparticle concentration is assumed to be 1% and 4% and Reynolds number is ranged from 100 to 800. The results show that the heat transfer enhancement by a using vortex generator and nanofluids is greater than the case of vortex generator and base fluid only, and the latest case provided higher enhancement of heat transfer compared to the case of a base fluid flowing in a plain duct. Considering the nanofluid as two separated phases is more reasonable than assuming the nanofluid as a homogeneous single phase. Temperature dependent properties model provided higher heat transfer and lower shear stress than the constant properties model.     

Reduction of power and lubricant oil consumption in milling process using a new SiO2 nanolubrication system

In this paper, we propose a method based on the surfaces enveloping theory developed as a vertical application in the CATIA graphical design environment. This method is created for profiling tools intended to generate cylindrical helical surfaces with constant pitch. The devised method is applicable for the profiling of disc tools which are bounded by a primary peripheral surface of revolution. A few examples for the determination of the tool’s 3D primary peripheral surface are presented such as helical flutes of cutting tools, worms with wide pitches, and gear involute flanks. The results are presented in both graphical and tabular form for completeness. Screen snapshots of the CATIA-based vertical application are also shown.     

An optimization method of the machining parameters in high-speed machining of stainless steel using coated carbide tool for best surface finish

High-speed machining (HSM) has emerged as a key technology in rapid tooling and manufacturing applications. Compared with traditional machining, the cutting speed, feed rate has been great progress, and the cutting mechanism is not the same. HSM with coated carbide cutting tools used in high-speed, high temperature situations and cutting more efficient and provided a lower surface roughness. However, the demand for high quality focuses extensive attention to the analysis and prediction of surface roughness and cutting force as the level of surface roughness and the cutting force partially determine the quality of the cutting process. This paper presents an optimization method of the machining parameters in high-speed machining of stainless steel using coated carbide tool to achieve minimum cutting forces and better surface roughness. Taguchi optimization method is the most effective method to optimize the machining parameters, in which a response variable can be identified. The standard orthogonal array of L₉ (3⁴) was employed in this research work and the results were analyzed for the optimization process using signal to noise (S/N) ratio response analysis and Pareto analysis of variance (ANOVA) to identify the most significant parameters affecting the cutting forces and surface roughness. For such application, several machining parameters are considered to be significantly affecting cutting forces and surface roughness. These parameters include the lubrication modes, feed rate, cutting speed, and depth of cut. Finally, conformation tests were carried out to investigate the improvement of the optimization. The result showed a reduction of 25.5% in the cutting forces and 41.3% improvement on the surface roughness performance.     

Prevalence of Listeria spp. in ready to eat foods (RTE) from Algiers (Algeria)

The aim of this study was to establish the occurrence of Listeria spp., especially Listeria monocytogenes in ready to eat RTE food marketed in Algiers (Algeria).A total of 227 samples were collected from different producers and retailers.All samples were analyzed using a conventional cultivation method AFNOR V08-055.Out of 227 samples tested, 21 (9.3%) tested positive for Listeria spp. among them, 6 (2.6%) tested positive for L. monocytogenes. L. innocua was the most common Listeria species found being detected in 11 samples (4.8%), although both Listeria ivanovii and Listeria welshimeri were detected in 3 (1.3%) and 1 (0.4%) food samples respectively.The study of the antimicrobial sensitivity of Listeria monocytogenes strains showed no resistance.The study has enabled us to detect these contaminants in a wide range of RTE foods, to suggest that contamination likely occurs after heat treatment, and to assess the danger represented by this category of food for populations at risk.     

Identification and molecular characterization of Listeria monocytogenes isolated in raw milk in the region of Algiers (Algeria)

Listeria monocytogenes was isolated from raw milk, whey and curdled milk produced and collected in the region of Algiers and Blida between September 2003 and July 2004. Four out of 153 (2.61%) farm milk samples and 6 out of 80 (7.50%) tankers' samples tested positive for L. monocytogenes. All samples of whey and curdled milk (n=12) tested negative for L. monocytogenes, but 2 of 22 (9%) samples of whey were contaminated by L. innocua. L. monocytogenes isolates were grouped by a multiplex PCR assay; all isolates belonged to the PCR-group IVb, which corresponds to serovars 4b, 4d and 4e. L. monocytogenes isolates were characterized by Pulsed-Field Gel Electrophoresis (PFGE). The combination of AscI and ApaI macrorestriction patterns yielded five different pulsovars (I to V). The results indicate that raw milk, and raw milk products are potential sources of the L. monocytogenes and represent a potential risk for consumers.     

Catalytic performance of organically templated nano nickel incorporated-rice husk silica in hydroconversion of cyclohexene and dehydrogenation of ethanol

Rice husk silica (RHS) was extracted from local rice husk by acid digestion and burning at 650 °C. RHS-Ni catalyst was prepared by dissolving RHS in 1 N NaOH and titrating with 3 N HNO₃ containing 10 wt.% Ni²⁺. The organic modifiers, either p-amino benzoic acid (A) or p-phenylenediamine (PDA) were incorporated in 5 wt.% and reduced in H₂ flow. Investigation of the three catalysts, (RHS-Ni)_R350, (RHS-Ni–A)_R350 and (RHS-Ni–PDA)_R350, confirmed good dispersion of Ni nanoparticles; all catalysts were amorphous. The BET surface areas increased in the order: (RHS-Ni)_R350 < (RHS-Ni–A)_R350 < (RHS-Ni–PDA)_R350 with controlled pore sizes. The as-prepared catalysts were applied for both hydroconversion of cyclohexene with molecular H₂ and ethanol dehydrogenation, using a flow-type reactor, at different temperatures. The activity in cyclohexene hydroconversion and selectivity to cyclohexane depended upon the reaction temperature; at t < 150 °C, the increased hydrogenation activity was referred to the formed SiO₂–Ni–amine complex, pore regulation as a prime requirement for H₂ storage and homogeneous distribution of incorporated Ni nanoparticles. At t > 150 °C, the backward dehydrogenation pathway was more favored, due to unavailability of H₂; the process became structure-sensitive. In ethanol conversion, the prevailing dehydrogenation activity of organically modified catalyst samples was encouraged by improved homogeneous distribution of Ni nanoparticles and created micropre system.